The First Interplanetary CubeSats Are Set to Fly to Mars

Early Saturday morning, an Atlas V rocket is scheduled to launch from Vandenberg Air Force Base in California carrying NASA's next mission to the surface of Mars, the InSight lander. InSight's main body is very similar to the Phoenix spacecraft that landed on Mars in 2008, and it will carry two primary science instruments to the Red Planet: a high-sensitivity seismometer to measure "marsquakes" (sensitive enough to detect the oceans from Colorado) and a heat probe attached to a self-hammering "mole" that will burrow 3 meters below the surface.

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With a better understanding of the interior geologic activity of Mars, scientists can continue to piece together a picture of the history of the planet, thought to have undergone a radical transformation from an atmosphere-protected world of running water billions of years ago to an irradiated, frigid desert today.

But InSight won't be making the trip to Mars alone. NASA's newest Mars mission is taking two little buddies along with it: the twin MarCO spacecraft, or Mars Cube One.

"MarCO is the first deep space CubeSat mission, which is very exciting for several reasons," says Anne Marinan, MarCO systems engineer at NASA JPL. "It's the first time that we're demonstrating the capabilities for satellites of this size with non-custom parts—parts you can buy from vendors. ... If it works, it has huge implications for future planetary missions in terms of capabilities that missions can bring along with them."

Engineer Joel Steinkraus with the two MarCO spacecraft at JPL, one with its antenna and solar panels deployed, the other folded up into launch configuration.

NASA/JPL-Caltech

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The MarCO CubeSats, measuring 36.6 cm x 24.3 cm x 11.8 cm, are technology demonstrator spacecraft that will fly on their own trajectories during the six-month trip to Mars. They will serve as a communications relay for the entry, descent, and landing (EDL) of the InSight mission. If all goes according to plan, the MarCO satellites will give the InSight team real-time information about the touchdown of the lander (accounting for an eight-minute delay for signals to travel from Mars to Earth).

"There will be two types of information: indications of major events accomplished, [such as] parachute deploy and final touchdown, and sensor data [including] temperature and estimated altitude during the descent through the Martian atmosphere," Marinan says.

Like the 2008 Phoenix landing, InSight will use small rockets to control its descent through the Martian atmosphere, deploy a parachute to decelerate, jettison its heat shield, deploy its shock-absorbing landing legs, and finally fire up 12 retro-rockets to achieve a soft landing. After soaring into the Martian sky at about 14,100 mph (6.3 kilometers per second), InSight will come to rest on the surface and sit as still as possible for two years, listening to the churnings of the Martian depths.

One of the primary challenges for small satellites in deep space is establishing a communications link. Historically, deep space communication has required large radio dishes to beam signals back to Earth. The MarCO CubeSats, however, are testing out a small, flat, high-gain, X-band antenna to relay data from InSight's landing back home.

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"There's a pattern embedded in the antenna itself," Marinan says. "It looks like a circular array of different sized copper squares, and so if you look at it from far away, you can kind of see a circular pattern in it, and that simulates the effect of a dish. So when an RF signal is reflected off of that surface, it acts like it reflected off a dish."

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The boxy little craft will unfold their solar panels shortly after being released from small dispensers on the bottom of the Centaur rocket stage, which will separate from the first stage of the Atlas V rocket about 4 minutes and 10 seconds after liftoff. After the solar panels are deployed, the MarCO sats will open their high-gain antennas "like a brochure" and establish communications with Earth. Reaction wheels on the CubeSats will be used to position their cold-gas thrusters for trajectory corrections along the way to Mars.

When InSight lands, MarCO will be there to broadcast it live, establishing an ultra high frequency (UHF) relay with the lander and transmitting X-band signals back to Earth. The Mars Reconnaissance Orbiter (MRO), a full-sized NASA spacecraft that has been orbiting Mars since 2006, will also be recording data from the landing, but it does not have the capability to receive and transmit at the same time. If the MarCO spacecraft should fail, JPL will have to wait hours to find out what happened to InSight, as MRO will sling around the far side of the Mars before it has a chance to transmit to the Deep Space Network (DSN) on Earth.

"If MarCO does survive and ends up doing the data relay with InSight, having a bring-your-own comm capability is a very cool enabling architecture," Marinan says. "Currently what Mars landers have to do is coordinate with these orbiters that are around Mars, and that requires the orbiter to make orbit corrections or stop the primary science mission to do data relay."

MarCO will also carry a wide-field camera to confirm successful deployment of the antenna and a narrow-field camera to snap photos of just about whatever the team can. "If we want to get pictures of Earth, or if it's still working by the time MarCO gets within range of Mars, getting a picture of Mars would be very cool," Marinan says.

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Diagram of the MarCO spacecraft.

NASA/JPL-Caltech

In the future, additional deep space CubeSats will likely follow in MarCO's footsteps. In addition to a "bring-your-own comm capability" for bigger missions, these small satellites could start doing science work all on their own. However, MarCO's cold-gas thrusters are not nearly sufficient to slow down enough to enter Mars orbit, and the little spacecraft will shoot on by after watching InSight touch down to continue orbiting the sun. To orbit other planets with CubeSats, we will need something with a little more oomph.

"I know of companies that are [working on] ion thrusters or electrospray thrusters, small Hall effect kind of thrusters, but also chemical propulsion," Marinan says. "There's a whole range of development for CubeSats and smallsats."

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If engineers can dial in small-but-powerful CubeSat thrusters, the possibilities for these little spacecraft really open up.

"If you could put it into orbit... there are several examples of remote sensing instruments that could be packaged to fly on small platforms like CubeSats and small satellites," Marinan says. "Low resolution compared to something like HiRISE imaging [on MRO]... but you can take multiple measurements with different satellites from different orbits. So kind of more measurements, maybe not as good. But having multiple and getting higher special and temporal resolution has a lot of science implications."

CubeSats are starting to replace the large bus-style spacecraft orbiting our planet, taking over jobs from Earth imaging to radar scanning to spectroscopy. As communications and small-scale propulsion technologies improve, swarms of these affordable little craft could explore the inner planets and the asteroid belt—perhaps eventually getting powerful enough to fly to the outer solar system as well.

"It would be a very cool paradigm shift if we can successfully demonstrate that it works," Marinan says.

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